1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive tape or sheet. More particularly, the invention relates to a pressure-sensitive adhesive tape or sheet which is moisture permeable and which scarcely causes an eruption (skin lesion) or irritation of the skin when it is applied on the skin for a long time.
2. Description of the Prior Art
Various polymeric compounds have heretofore been used as adhesives for pressure-sensitive adhesive tapes or sheets. For example, there can be mentioned copolymers comprising an alkyl acrylate as the main component, vinyl acetate-ethylene copolymers, natural rubbers, sulfur-cross-linked natural rubbers and polyisoprenes. Pressure-sensitive adhesive tapes and sheets which possess excellent properties, such as adhesiveness and weatherability, are prepared and used in various fields. However, when these adhesive tapes or sheets are used on the human body, i.e., as bandages or wrappings, they readily cause eruption or irritation of the skin. Elimination of this defect has been eagerly desired.
Japanese Patent Publication (Kokai) No. 97059 of 1974 discloses an air-permeable pressure-sensitive tape coated with an adhesive composition consisting of 90-99% by weight of a copolymer, a primary component of which is an alkyl acrylate having an alkyl radical of at least 4 carbon atoms, and 10-1% by weight of hydroxyethyl cellulose.
Japanese Patent Pubilication (Kokai) No. 49336 of 1975 discloses an air-permeable pressure-sensitive tape or sheet coated with an adhesive composition consisting of:
(A) 90-99% by weight of a copolymer consisting of 85-99% by weight of an alkyl acrylate having an alkyl radical of at least 4 carbon atoms, and 1-15% by weight of a compound copolymerizable with said alkyl acrylate, and PA0 (B) 10-1% by weight of hydroxyethyl cellulose.
It has been considered that the causes of skin eruption or irritation resulting from the use of adhesive plasters include a physical cause, namely, the damage of the horny layer of the skin surface caused by peeling of the tape or the like from the skin surface, a chemical cause, namely, a primary irritation by or an allergic reaction to the adhesive, and a physiological cause, namely, inhibition of the evaporation of water (skin respiration) caused by blocking of the sweat openings on the skin surface. Among these causes, the physiological cause is most serious. More specifically, a pressure-sensitive adhesive tape or sheet is poor in air permeability, moisture permeability and/or moisture absorbing property. When it is applied to the skin, it causes clogging of sweat openings on the skin surface. It is considered that this action is a main cause of skin eruption or irritation resulting from the use of adhesive plasters. As a means for eliminating this defect, there has been proposed a method in which fine apertures are formed in the pressure-sensitive adhesive tape or sheet, which apertures extend through the adhesive layer thereof. In a pressure-sensitive adhesive tape or sheet prepared according to this method, however, although the aperture portions provide air permeability and moisture permeability, other portions of the tape or sheet are still in the closed or impervious state and hence, the effect of preventing skin eruption or irritation is insufficient. Further, from the technical veiwpoint, this method is still disadvantageous in that the formation of the required fine apertures is quite difficult in the case of an adhesive plaster having a substantial thickness, particularly a thick adhesive layer.